Open access

TRAPPIST (TRAnsiting Planets and PlanetesImals Small
Telescope)
E. Jehin, M. Gillon, C. Opitom, J. Manfroid, D. Hutsemékers, L. Delrez, P. Magain
Département d'Astrophysique, de Géophysique et d'Océanographie, Université de Liège, Allée du six Août, 4000 Liège,
Belgium ([e-mail])
Abstract
TRAPPIST is a 60-cm robotic telescope that has
been installed in June 2010 at the ESO La Silla
Observatory [1]. Operated from Liège (Belgium) it is
devoted to the detection and characterisation of
exoplanets and to the study of comets and other small
bodies in the Solar System. We describe here the
hardware and the goals of the project and give an
overview of the comet production rates monitoring
after three years of operations.
1. The TRAPPIST project
TRAPPIST (TRAnsiting Planets and PlanetesImals
Small Telescope) is a project driven by the
Astrophysics and Image Processing group (AIP) at
the Department of Astrophysics, Geophysics and
Oceanography (AGO) of the University of Liège
(Belgium), in close collaboration with the
Observatory of Geneva (Switzerland). The science
goal of TRAPPIST is the study of planetary systems
through two approaches: the detection and study of
exoplanets and the study of comets, asteroids and
TNO.
1.1 The telescope and observatory
TRAPPIST’s optical tube unit is a Ritchey-Chretien
0.6 meter telescope with a focal length of 4.8 meter.
It is associated with a German equatorial mount that
is, thanks to its direct drive system, extremely fast
(up to 50 deg/sec), accurate (tracking accuracy
without autoguider better than 10” in 10 min), and
free of periodic error. The instrument is a Peltier-
cooled commercial camera equipped with a Fairchild
3041 back-illuminated 2k × 2k chip. The pixel scale
is 0.64”/pixel. Three read-out modes are available,
the shortest read-out time being 2s. The total field of
view of the camera is 22’ × 22’. It is associated to a
custom-made dual filter wheel. One of the filter
wheel contains broad band filters for the exoplanet
photometry (Johnson B, V, R, Cousins Ic, Sloan z′,
and a special I+z filter), while the other contains the
narrow-band NASA HB cometary filters (OH, UC,
NH, CN, CO+, C3, CN, BC, C2 , GC, RC and a NaI
filter) [2].
The telescope is protected by a 5 meter diameter
dome that was totally refurbished and automatized
early 2010. The observatory is fully robotic and
equipped with a weather station, an UPS and
webcams.
Figure 1. TRAPPIST at ESO la Silla Observatory
2. Comet monitoring
For relatively bright comets (V < 12) we measure
several times a week the gaseous production rates
(using a Haser model) and the spatial distribution of
several species among which OH, NH, CN, C2 and
C3 as well as ions like CO+. The dust production
rates (Afrho) and color of the dust are determined
through four dust continuum bands (UC, BC, GC,
RC). Such regular measurements are rare because of
EPSC Abstracts
Vol. 8, EPSC2013-968, 2013
European Planetary Science Congress 2013
c
Author(s) 2013
EPSC
European Planetary Science Congress

the lack of observing time on larger telescopes. Yet
they are very valuable as they show how the gas
production rate of each species evolves with respect
to the distance to the Sun. Those observations allow
to determine the composition of the comets and the
chemical class to which they belong (rich or poor in
carbon for instance [3]), possibly revealing the origin
of those classes but also if there are some changes of
the abundance ratios along the orbit (evolutionary
effects). Indeed with half a dozen of comets observed
each year - and as long as possible along their orbit -,
this program will provide a good statistical sample
after a few years. We will present the first results of
this monitoring.
Thanks to the way the telescope is operated, follow-
up of split comets and of special outburst events is
possible right after an alert is given and can bring
important information on the nature of comets, like
for comet C/2010 G2 (Hill) in December 2011.
In addition to providing the productions rates of the
different species through a proper photometric
calibration, image analysis can reveal coma features
(jets, fans, tails), that can lead to the detection of
active regions and measure the rotation period of the
nucleus.
The monitoring is also useful to assess the gas and
dust activity of a given comet in order to prepare
more detailed observations with larger telescopes.
Such data can be obtained at any time under request.
Finally a dozen of faint comets (V < 20) are
monitored once a week through B, V, Rc, Ic filters
and magnitudes and positions are sent to the MPC.
Acknowledgements
E.J. and M.G. are Research Associate FNRS, C.O is
FNRS Research Fellow, D.H. is Senior Research
Associate at the FNRS, J.M. is Research Director of
the FNRS, and P.M. is Professor.
We would like to thank David Schleicher from
Lowell Observatory for having recovered and lent
one complete set of NASA cometary filters.
References
[1] Jehin et al., The Messenger, 145, 2-6, 2011.
[2] Farnham et al., Icarus, 147, 180-204, 2000.
[3] A'Hearn et al., Icarus, 118, 223-270, 1995.